This invention relates to a process for producing L-tryptophan, L-tyrosine or L-phenylalanine by fermentation. L-tryptophan is an amino acid useful as a medicament, food, an additive for animal feed, etc.; L-tyrosine is an amino acid useful especially as a medicament; and L-phenylalanine is an amino acid useful in the pharmaceutical and food industries.
Heretofore, various processes for producing L-tryptophan by fermentation using coryneform glutamic acid-tryptophan producing bacteria have been known; for example, a process using a microorganium belonging to the genus Corynebacterium, requiring L-tyrosine and L-phenylalanine and being resistant to at least of tyrosine analogues and phenylalanine analogues (Japanese Published Examined Patent Application No. 19037/1976); a process using a microorganism resistant to tryptophan analogues, such as 5-methyltryptophan (Japanese Published Examined Patent Application Nos. 18828/1973, 38795/1976 and 39517/1978); a process using a microorganism requiring histidine (Japanese Published Examined Patent Application No. 4505/1972); and a process using a Brevibacterium strain whose pyruvate kinase activity is decreased or lacked (Japanese Published Unexamined Patent Application No. 25339/1987).
Further, various processes for producing L-tyrosine or L-phenylalanine by fermentation using coryneform glutamic acid-producing bacteria have been known; for example, a process using an auxotrophic mutant strain requiring amino acids, a mutant strain resistant to amino acid analogues, a mutant strain whose pyruvate kinase activity is decreased or lacked, or a strain having these properties simultaneously [Nippon Nogeikagaku Kaishi, 50 (1), p.R 79 (1979); Japanese Published Unexamined Patent Application No. 128897/1986].
On the other hand, microorganisms capable of producing L-tyrosine or L-phenylalanine have been constructed by recombinant DNA technique. As an example of L-tyrosine-producing microorganism, a strain carrying a recombinant DNA containing a gene coding for 3-deoxy-D-arabino-hepturosonate-7-phosphate synthase (hereinafter referred to as DS), a gene coding for chorismate mutase (hereinafter referred to as CM) and a gene coding for prephenate dehydrogenase or pretyrosine aminotransferase, is known (Japanese Published Unexamined Patent Application No. 34197/1985). As an example of L-phenylalanine-producing microorganism, a strain carrying a recombinant DNA containing a gene coding for DS or genes coding for CM and prephenate dehydratase (hereinafter referred to as PD), are known (Japanese Published Unexamined Patent Application Nos. 24192/1985, 260892/1986 and 124375/1986).
With the recent increase in the demand for L-tryptophan, L-tyrosine and L-phenylalanine, improved processes for the industrial production thereof are desired.
As a result of intensive studies to obtain a new strain with higher L-tryptophan, L-tyrosine or L-phenylalanine productivity, the present inventors have found that if strains of coryneform glutamic acid-producing bacteria that are capable of producing L-tryptophan, L-tyrosine or L-phenylalanine are mutated to be decreased or lacked in phosphoenolpyruvate carboxylase (EC. 4.1.1.31) (hereinafter referred to as PC) activity, they acquire high productivity of these amino acids.